Handle "connection refused" when sending a uevent

This error was already being handled on the `connect` call right above
these changes, but wasn't being handled on the call to `sendmsg`.
Depending on the timing it was possible for the `connect` call to
succeed while the `sendmsg` call failed with an ECONNREFUSED error
leading to the test crashing from the abort call.

src/uevent_sender.c

@@ -100,8 +100,14 @@ sendmsg_one(struct iovec *iov, size_t iov_len, const char *path)
     const struct msghdr msg = { .msg_name = &event_addr, .msg_iov = iov, .msg_iovlen = iov_len };
     ssize_t count = sendmsg(fd, &msg, 0);
     if (count < 0) {
-        perror("uevent_sender sendmsg_one: sendmsg failed");
-        abort();
+	if (errno == ECONNREFUSED) {
+	    /* client side closed its monitor underneath us, so clean up and ignore */
+	    unlink(event_addr.sun_path);
+	    close(fd);
+	    return;
+	}
+	perror("uevent_sender sendmsg_one: sendmsg failed");
+	abort();
     }
     /* printf("passed %zi bytes to event socket %s\n", count, path); */
     close(fd);